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In Tuesday’s election, House districts on the outskirts of major American cities were the site of electoral shifts that propelled Democrats to power.

Wealthy and middle class voters delivered the suburban votes for enough Democratic pickups to secure a majority. In several cases, the battleground districts were wealthy and highly educated places that Hillary Clinton won in 2016, exposing the vulnerability of those Republican lawmakers.

Democrats dominate in wealthy districts

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Uncalled races not shown. No PA flips are noted; the state’s congressional lines were redrawn.

The precinct-level results shown on the maps in this story show the most precise view of how voters within a district swung. This level of detail can also provide more insight into what caused a district to flip — or not.

These maps show how those neighborhoods handed Democrats the House.

We’ll start in Virginia’s 7th District, where Rep. Dave Brat (R) was challenged by ex-CIA operative Abigail Spanberger (D). This north-south district goes from above Culpeper to rural areas near the southern border of the state, but the voters are concentrated in the suburbs of Richmond and Fredericksburg.

Here are precinct-level results for the 2016 presidential election, with circles sized based on the margin of victory for the Democrat or Republican in each precinct.

The district backed Donald Trump by six percentage points in 2016. Democratic margins around Richmond were outweighed by the Republican tilt of the rest of the district.

But in 2018, those Fredericksburg and Richmond suburbs flipped to Spanberger, securing her the win.

In 2018, Brat’s support in wealthier neighborhoods softened ...

...while middle-class voters surged for Spanberger. Remember that there are many more voters around the cities in the east part of the district.

As with many of the districts shown here, the 7th District voted overwhelmingly for Mitt Romney, but less favorably for Trump.

“These are places that just don’t like the president that much, and I think that’s reflected in this House vote,” said Kyle Kondik, managing editor at the nonpartisan political analysis site Sabato’s Crystal Ball.

Virginia Democrats also flipped the D.C.-area 10th District, the wealthiest Republican-held House district, thanks to similar voting patterns. Notice the Democratic advantages in the eastern half of the district, closer to the city.

Now let’s look at a former Republican stronghold near Dallas. In 2016, the 32nd District backed Clinton by 1.9 points, shown on the map. But voters simultaneously reelected Rep. Pete Sessions, a longtime Republican congressman. Democrats hadn’t even fielded a challenger to Sessions that year.

This time, Sessions fared even worse than Trump did. He lost 52 percent to 46 percent to Democrat and former NFL player Colin Allred. In district after district, Clinton’s result foreshadowed a House GOP loss.

By 2018, high-income voters in this district dropped to relatively narrow margins (they had voted 2-to-1 for Romney), taking away Sessions’s safety cushion.

The middle-income neighborhoods split evenly in recent presidential elections. However, their 60 percent to 40 percent break for Allred helped him score a six percentage point win districtwide.

Now let’s look at the rapidly changing area north of Atlanta in Georgia’s 6th District. Trump won narrowly here, and Rep. Karen Handel (R) won a closely watched special election in 2017.

In 2018, Democrat Lucy McBath, a gun control activist who lost her son to gun violence, was able to shrink the Republican advantage among wealthy precincts even further. It continued a trend: Whereas President Barack Obama lost wealthy precincts here by about 80,000 voters in 2012, Clinton only lost them by 23,000.

McBath also drove up margins in the middle-class precincts, securing a tight victory on Thursday.

On the West Coast, Russia-friendly Rep. Dana Rohrabacher (R) was slightly behind as more votes were being counted. Rohrabacher, a 15-term congressman, faced Harley Rouda, a businessman and former Republican who won his primary by only 125 votes.

This very wealthy district has a lot of high-income voters. Although they had previously given Republicans an insurmountable advantage in this district, they split 50-50 in 2018, taking away the 40,000-vote margin Romney had captured.

And here’s why Rohrabacher could be headed for defeat as more votes are counted: Middle-class voters gave Rouda an edge. His lead over the Republican grew on Thursday.

And finally, in the Minnesota 3rd, Rep. Erik Paulsen (R) lost the affluent suburban district by more than 10 points to Dean Phillips, a businessman who worked to tie Paulsen to Trump. (In 2016, Paulsen had won by almost 14 points.)

In this case, note how closely the 2018 map mirrors the Clinton-Trump contest. With several races still undecided, Democrats have already won more than half of the 23 Republican districts that Clinton won, including two in the state.

“For Minnesota, the changes from 2016 to 2018 were really bringing the congressional districts in line with the presidential voting in those districts,” said Kathryn Pearson, an associate professor of political science at the University of Minnesota. Republicans in the state also won two Democrat-held seats that Trump won in 2016.

Pearson credited Paulsen’s defeat to his association with the president. “His rhetoric is very moderate, but his voting record was right in line with Trump and that was really the key issue in the campaign.”

But both this district and the nearby 2nd District voted Democratic this year, completing the movement left. Wealthy voters have moved from Republican bastions to Democratic centers. They had each given Romney a winning margin of about 15,000 votes.

At the same time, middle-income neighborhoods stayed reliably Democratic, creating districts that Republicans will be challenged to capture back.

Tim Meko, Ted Mellnik and Laris Karklis contributed to this report.

About this story

Precinct results from state and local election officials, gathered by Decision Desk HQ and The Washington Post. Race and ethnicity population data comes from the the five-year 2012-2016 American Community Survey.

Wealthy precincts are defined as precincts with a median household income of more than $75,000. Middle-class precincts fall between $40,000 and 75,000.